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151.
152.
铜在HOPG上电沉积过程的现场ECSTM研究 总被引:3,自引:1,他引:3
用自制的电化学扫描隧道显微镜(ECSTM)现场研究Cu在HOPG上的电沉积过程.结果表明Cu在HOPG上的电沉积为三维成核的过程.当电位较低或Cu2+离子浓度较低时,铜在本体金属生长主要沿着台阶方向.过电位较高时,铜的成核数目增加,沉积层的晶粒有所细化.同时,非现场ECSTM比较研究表明,STM针尖对针尖局部区域的电沉积起屏蔽作用,针尖所在区域Cu的沉积速度比其它区域明显减小 相似文献
153.
A novel method for monitoring of mutagenic process of dimethyl sulfate to Salmonella typhimurium strain (TA100) was proposed by using piezoelectric quartz crystal impedance (PQCI) analysis technique. The time courses of responses piezoelectric impedance parameters for a quartz crystal in a culture system were simultaneously obtained and discussed. It was found that the motional resistance variation (DeltaR(m)) increases and frequency shift (Deltaf) of PQC sensor decreases correspondingly during the mutagenic process of the bacteria. These parameters could reflect the variations of viscosity and density of culture system. By fitting DeltaR(m) versus time curves toward Gompertz bacterial growth model, we obtained and discussed the bacterial growth parameters for both normal growth and mutagenic process. The experiments showed that the proposed method could provide real time and multidimensional impedance information to the monitoring of mutagenic process. 相似文献
154.
Zhi C Bando Y Tang C Xie R Sekiguchi T Golberg D 《Journal of the American Chemical Society》2005,127(46):15996-15997
We report for the first time that boron nitride nanotubes (BNNTs) may be dissolved in organic solvents by wrapping them with a polymer. Transmission electron microscopy and cathodoluminescence studies indicate the strong pi-pi interactions between BNNTs and the polymer. A band gap ranging from 5.2 to 5.5 eV was documented for the BNNTs independent of their geometrical characteristics by using ultraviolet-visible absorption experiments on composite films and thin BNNT films prepared from solutions. 相似文献
155.
Transformation of arctiin to estrogenic and antiestrogenic substances by human intestinal bacteria 总被引:2,自引:0,他引:2
Xie LH Ahn EM Akao T Abdel-Hafez AA Nakamura N Hattori M 《Chemical & pharmaceutical bulletin》2003,51(4):378-384
After anaerobic incubation of arctiin (1) from the seeds of Arctium lappa with a human fecal suspension, six metabolites were formed, and their structures were identified as (-)-arctigenin (2), (2R,3R)-2-(3',4'-dihydroxybenzyl)-3-(3",4"-dimethoxybenzyl)butyrolactone (3), (2R,3R)-2-(3'-hydroxybenzyl)-3-(3",4"-dimethoxybenzyl)butyrolactone (4), (2R,3R)-2-(3'-hydroxybenzyl)-3-(3"-hydroxy-4"-methoxybenzyl)butyrolactone (5), (2R,3R)-2-(3'-hydroxybenzyl)-3-(3",4"-dihydroxybenzyl)butyrolactone (6), and (-)-enterolactone (7) by various spectroscopic means including two dimensional (2D)-NMR, mass spectrometry, and circular dichroism. A possible metabolic pathway was proposed on the basis of their structures and the time course of the transformation. Enterolactones obtained from the biotransformation of arctiin and secoisolariciresinol diglucoside (SDG, from the seeds of Linum usitatissium) by human intestinal bacteria were proved to be enantiomers, with the (-)-(2R,3R) and (+)-(2S,3S) configurations, respectively. Compound 6 showed the most potent proliferative effect on the growth of MCF-7 human breast cancer cells in culture among 1 and six metabolites, while it showed inhibitory activity on estradiol-mediated proliferation of MCF-7 cells at a concentration of 10 microM. These results indicate that the transformation of 1 by intestinal flora might be essential for the manifestation of the estrogenic and antiestrogenic activity of 1. 相似文献
156.
由聚苯胺粒子组成的电流变液的研究 总被引:6,自引:1,他引:6
由经碱处理的掺杂态聚苯胺(PAn)制得高介电常数的半导体PAn粒子,将其悬浮于电绝缘油可组成电流变液,讨论了电流变(ER)液的静态屈服应力(τ_s),电流密度等性能与PAn的介电常数(ε_p),导电率(σ),体积分数和应用电场强度的关系。对导电率相同的PAn粒子,用氨水处理的PAn粒子ε_p较用NaOH液处理的高,前者在σ足够低如σ≤1.0×10 ̄(-7)/cm时,ER液的τ_s随偶极系数的平方(β ̄2)的增大而呈现非线性增加;后者ER液的τ_s随β ̄2的增大出现一最大值.结果表明:由聚苯胺粒子可组成高电流变活性的无水ER液. 相似文献
157.
The piezoelectric quartz crystal (PQC) impedance technique was applied to monitor in situ generation and precipitation of the ferric hydroxide sol in aqueous solutions at 90 degrees C. Equivalent circuit parameters and resonant frequencies as well as the half-peak width of the electroacoustic conductance spectrum deltaf(G1/2) for the PQC resonance were obtained and analyzed. Three stages, sol generation and simultaneous adsorption, adsorption equilibrium, and precipitation of ferric hydroxide sol could be identified in the process of adding the ferric nitrate solution into the hot water. A scheme of two consecutive reactions occurring at the electrode/solution interface was used to analyze the adsorption kinetics of ferric hydroxide sol onto the Au electrode. In addition, the electrolyte-induced precipitation of the colloid was monitored and discussed. Temperature effect on the PQC resonance behavior in liquid was also investigated. Since the PQC impedance technique provides multidimensional piezoelectric information in situ, it is highly recommended for studying the process of sol-gel generation and precipitation. Copyright 2001 Academic Press. 相似文献
158.
Remarkably stable mesoionic oxazolones possessing an oxazolo[3,2-a]quinolinium structure (5a–b),8,16, 17) were obtained by the double cyclisation of phenylglycine-o-carboxylic acids (3a–c) in refluxing acetic anhydride or in benzoic anhydride at 140°, The 0-Ac group was eliminated to give the corresponding lactones (6a–b) or replaced by O-Ts (7). IR stretching vibrations of the endo-carbonyl were in the range 1710–1768 cm?1, while v1-CH exhibited unusually high values (3159–3194 cm-1). 1-Acyl derivatives could be obtained only with TFAA (23–24), although easy deuteration of the same position took place in the presence of traces of trifluoroacetic acid. Hydrolysis of 5b led to the α-quinolone-N-acetic acid 27a. In the case of 5a, hydrolysis was accompanied by self-acylation of the nucleophilic site at C-4 with formation of a dimeric acid 28a. The presence of an additional Me group in phenylalanine-o-carboxylic acid (36) activates the corresponding mesoionic oxazolone 37 so that 1-acylation becomes possible with formation of the fused oxazole 38 by the Dakin-West reaction. Temperature dependent magnetic non-equivalence of methylene protons has been observed in acids 3b-d and f and also in the 7-membered anhydride 48b. 相似文献
159.
Xianmei Xie Xiurong Ren Jinping Li Xiaojun Hu Zhizhong Wang 《天然气化学杂志》2006,15(2):100-104
Ultrasonic technology has been intensively studied recently due to its special features. In this paper, an ultrasonic crystallization method was introduced for the preparation of ZnAl-Hydrotalcite-Like compounds (ZnAl-HTLcs). Samples with high crystallinity, small particle size and narrow particle size distribution were obtained and fully characterized using conventional techniques of XRD, FT-IR and TGDTA. The results prove that both ultrasonic frequency and ultrasonic power have effects on the sizes of the product particles. By varying the ultrasonic power from 250 W to 88 W, with the ultrasonic frequency fixed at 59 kHz, the median particle size of the samples increased from 0.37 μm to 0.82 μm. By altering the hydrothermal treatment time from 1 h to 5 h at 110℃, the median particle size of ZnAl-HTLcs synthesized via ultrasonic crystallization increased from 0.88 μm to 1.11 μm. 相似文献
160.
Here we report the formation and spectroscopic properties of cadmium sulfide (CdS) nanocrystal systems: individual nanocrystal and CdS aggregates. The optical absorption and luminescence spectra of the aggregated CdS nanocrystals and individual nanocrystal show exciton aggregate and individual exciton characteristics. Although it is not Bose-Einstein condensation, such aggregated quantum dots (QDs) seem to supply us opportunity to study the interactions and condensation of excitons in multi-QDs system, not in the separated QDs system. 相似文献